Process for the preparation of 1-monoalkyl dimethylsilylpropyne polymers

ABSTRACT

A process for the preparation of 1-monoalkyl(C 1  -C 4 ) dimethylsilyl-1-propyne polymers which comprises polymerizing a 1-monoalkyl (C 1  -C 4 )dimethylsilyl-1-propyne monomer in the presence of a compound of a transition metal and a member selected from α,ω-dihydropolydialkylsiloxanes and polyalkylhydrosiloxanes in a solvent inert to the polymerization. The polymerization reaction proceeds at low temperatures in an efficient manner. Membranes of the resultant polymer have a high gas transmission and suffer but little degradation when placed under severe temperature conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application serial No.07/402,419, filed on Sep. 5, 1989.

FIELD OF THE INVENTION

This invention relates to a process for the polymerization of1-monoalkyl(C₁ -C₄)dimethylsilyl-1-propynes.

BACKGROUND ART

A variety of processes for the preparation of polymers of acetylenecompounds have been known and investigated. These processes commonlyhave several problems such as difficulty in obtaining high molecularweight polymers and low yield.

On the other hand, few studies on the polymerization of1-monoalkyldimethylsilyl-1-propynes which are one of di-substitutedacetylene compounds have been made since they have poor reactivity. Inrecent years, however, Higashimura et al developed catalysts effectivefor obtaining high molecular weight polymers of the propynes. This isknown from U.S. Pat. No. 4,755,193 and Japanese Laid-open PatentApplication No. 59-155409. In these publications, it is stated thatpolymers of 1-monoalkyl(C₁ -C₄)dimethylsilyl-1-propynes are obtained bypolymerization of 1-monoalkyl(C₁ -C₄)dimethylsilyl1-propynes in thepresence of a transition metal compound of Group V of the PeriodicTable. In this process, a relatively high polymerization temperature isused ranging from 30° to 100° C., within which the higher temperature isfavored and a long reaction time of from 12 to 36 hours is necessary.The 1-trimethylsilyl-1-propyne polymer obtained by the above process hasa very high gas permeability but its characteristic properties degradedconsiderably. This is reported by Higashimura et al (Journal of AppliedPolymer Science, JAPS, Vol. 30, p. 1655, 1985). According to thisliterature, when the polymer is thermally treated at 100° C. for about 5hours, the oxygen permeability coefficient (Po₂) is reduced to 1/5 ofthe initial value.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a process forthe polymerization of 1-monoalkyl(C₁ -C₄)dimethylsilyl-1-propyne, whichovercomes the drawbacks of the prior art process and wherein theresultant polymer exhibits stable gas permeability with a much reduceddegree of degradation of its characteristic properties.

It is another object of the invention to provide a process for thepreparation of 1-monoalkyl(C₁ -C₄)dimethylsilyl-1-propyne polymerswherein the polymers are efficiently obtained at relatively lowtemperatures within a shorter time than in the prior art process.

The polymerization reaction is performed in a solvent. Examples of thesolvent include aromatic hydrocarbons such as benzene, toluene, xyleneand the like; halogenated hydrocarbon such as 1,2-dichloroethane, carbontetrachloride, chloroform, 1,2,3-trichloropropane, trichloroethylene,chlorobenzene and the like; alicyclic hydrocarbons such as cyclohexane,cyclohexene and the like, and mixtures thereof. The monomerconcentration in the polymerization reaction is generally from 0.1 to 2moles per liter of the solvent, preferably from 0.3 to 1 mile per literof the solvent.

The order of addition of the solvent, monomer, compound of a transitionmetal of Group V and α,ω-dihydropolydialkylsiloxane andpolyalkylhydrosiloxane is not critical. In general, a transition metalcompound and an α,ω-dihydropolydialkylsiloxane and/orpolyalkylhydrosiloxane are first added to a solvent in predeterminedamounts and heated to about 60° C. for 5 to 15 minutes. During thistreatment, it is assumed that the transition metal is reduced with thehydrogen bonded to the silicon atoms of the siloxane compound orpolymer, thereby forming a reaction product serving as a polymerizationinitiator. Thereafter, the mixture is cooled down to about 0° C., towhich a predetermined amount of monomer is added. The polymerizationreaction may proceed at temperatures not higher than 0° C. and iscompleted in about 1 hour to several hours at a temperature of 30° C.The reaction temperature is generally in the range of from 0 to 80° C.,preferably from 30 to 70° C. Higher temperatures may be used but are noteconomical.

Alternatively, an α,ω-dihydropolydialkylsiloxane and/orpolyalkylhydrosiloxane may be added after keeping a solution of themonomer and the transition metal compound at a given temperaturesufficient to cause the reaction between the transition metal and thesiloxane.

The reaction solution obtained after completion of the polymerizationmay be purified by a so-called re-precipitation technique wherein thesolution is added to a large amount of a poor solvent therebyprecipitating the resultant polymer. Examples of the poor solventinclude alcohols such as methanol, ethanol and the like.

It will be noted that although the polymerization may be effected in anatmosphere of air, it is usually effected in an atmosphere of an inertgas such as nitrogen.

The polymer obtained by the polymerization process of the invention isvery high in molecular weight, e.g., not only does the polymerizationreaction solution become very viscous, but the reaction may also proceedto an extent where a solid product is obtained. In the latter case, thereaction system is diluted with a solvent and subjected tore-precipitation.

The gel permeation chromatography of the polymer reveals that its weightaverage molecular weight (Mw) is about 1,000,000 or over.

The polymer obtained by the above process is film-forming. When the filmobtained from the polymer is thermally treated at 100° C. for 5 hours asreported by Higashimura et al set out above, the oxygen permeabilitycoefficient undergoes but little degradation. The reason for this is notclear. Several factors may be considered including a structural changeof the polymer because of the presence of anα,ω-dihydropolydialkylsiloxane and/or polyalkylhydrosiloxane in thereaction system, a change in the cis-trans structure of the double bondsin the propyne compound owing to the polymerization reaction at lowtemperatures, e.g. at room temperature, and a very high degree ofpolymerization taking place. In any event, the final polymer product hasa high gas permeability and a very small degree of characteristicdegradation, thus being useful in practical applications. The polymersobtained by the process of the invention have utility not only as a gaspermeation membrane, but also as electronic and insulating materials.

The present invention is more particularly described by way of examples,

EXAMPLES 1-6

200 ml of purified toluene, 2 mmols of tantalum pentachloride (TaCl₅) asa compound of a metal of Group V and 0.5 g of polyalkylhydrosiloxane(SH-1107, available from Toray Silicone Co., Ltd.) were charged in anatmosphere of dry nitrogen onto a three-necked flask equipped with anagitator, a thermometer and a separatory funnel and having a capacity of300 ml, followed by heating to 60° C. for 10 minutes. Thereafter, themixture was cooled down to 0° C. (ice bath), and then 0.2 moles of1-trimethylsilyl-1-propyne was added, followed by polymerization for 3hours under agitation. A very viscous polymer solution was charged intoa large amount of methanol to obtain a polymer precipitate.

The thus obtained polymer was purified by re-precipitation, after whichthe molecular weight and gas permeation characteristic were measured. Asa result, the weight average molecular weight was 1,200,000 whendetermined by gel permeation chromatography using polystyrene as areference and the oxygen gas permeability coefficient was 1.46×10-⁶cc.cm/cm².sec.cmHg.

The above procedure was repeated using different transition metalcompounds and/or different polyalkylhydrosiloxane as shown in Examples2-6. The results are shown in the table below.

                                      TABLE                                       __________________________________________________________________________         Transition                                                                          Polymethyl-                                                                             Weight Average                                                Metal hydro-    Molecular Weight                                         Example                                                                            Compound                                                                            siloxane  --Mw     .sup.--Po.sub.2 *.sup.1                         __________________________________________________________________________    1    TaCl.sub.5                                                                          SH-1107   1,200,000                                                                              1.46 × 10.sup.-6                          2    NbCl.sub.5                                                                          SH-1107   1,200,000                                                                              8.6 × 10.sup.-7                           3    NbBr.sub.5                                                                          SH-1107   1,000,000                                                                              7.6 × 10.sup.-7                           4    TaCl.sub.5                                                                          KF-99*.sup.2                                                                            1,500,000                                                                              1.6 × 10.sup.-6                           5    TaCl.sub.5                                                                           ##STR1## 1,100,000                                                                              1.2 × 10.sup.-6                           6    TaCl.sub.5                                                                          PS 120*.sup.3                                                                           2,000,000                                                                              2.0 × 10.sup.-6                           __________________________________________________________________________     Note                                                                          *.sup.1 oxygen permeability coefficient (cc · cm/cm.sup.2            · sec · cmHg)                                               *.sup.2 KF 99 is a polymethylhydrosiloxane available from SinEtsu Silicon     Co., Ltd.                                                                     *.sup.3 PS 120 is a polymethylhydrosiloxane available from Chisso Co.,        Ltd.                                                                     

Similar results were obtained when the general procedure of the aboveexamples was repeated using polydimethylsiloxane terminated withhydrogen at both ends (PS-537, available from Petrarch System, Inc., ofU.S.A.).

What is claimed is:
 1. A process for the preparation of 1-monoalkyl (C₁-C₄)dimethylsilyl-1-propyne polymers which comprises polymerizing a1-monoalkyl(C₁ -C₄)dimethylsilyl-1-propyne monomer in the presence of acompound of a transition metal of Group V of the Periodic Table and amember selected from the group consisting ofα,ω-dihydropolydialkylsiloxanes and polyalkylhydrosiloxanes in a solventinert to the polymerization.
 2. A process according to claim 1, whereinsaid 1-monoalkyl(C₁ -C₄)dimethylsilyl-1-propyne monomer istrimethylsilyl-1-propyne.
 3. A process according to claim 1, whereinsaid compound is a halide of a transition metal.
 4. A process accordingto claim 1, wherein said transition metal compound is used in an amountof from 0.01 to 10 mole % based on the monomer.
 5. A process accordingto claim 1, wherein said member is an α,ω-dihydropolydialkylsiloxane ofthe following formula: ##STR2## wherein each R represents an alkyl grouphaving 1 to 8 carbon atoms, and n is an integer of 1 to
 8. 6. A processaccording to claim 5, wherein the siloxane is used in an amount of from1 to 10 mole %, as the hydrogen atom bonded directly to the siliconatoms at both ends based on the monomer.
 7. A process according to claim5, wherein each R is a methyl group.
 8. A process according to claim 1,wherein said member is a polyalkylhydrosiloxane of the followingformula: ##STR3## wherein each R' represents an alkyl group having 1 to8 carbon atoms and m is an integer of not less than
 1. 9. A processaccording to claim 8, wherein said polyalkylhydrosiloxane is used in anamount of from 1 to 10 mole %, as the hydrogen atom bonded directly tothe silicon atom or atoms, based on the monomer.
 10. A process accordingto claim 8, wherein each R' is a methyl group.
 11. A process accordingto claim 1, wherein the polymerization is effected at a temperature offrom 0° to 80° C.
 12. A process according to claim 11, wherein thetemperature is from 30° to 70° C.
 13. A process according to claim 1,wherein said compound and said member are first added to the solvent andheated up to 60° C. and cooled, after which said monomer is polymerized.14. A process according to claim 1, further comprising charging theresultant reaction solution into a large amount of a poor solvent,thereby precipitating a polymer formed by the polymerization.
 15. Aprocess according to claim 1, wherein the monomer is added in an amountof 0.1 to 2 moles per liter of the solvent.